Peru 1999.

Methods	A double‐blind, RCT.
Participants	1295 women with a low‐risk pregnancy (uncomplicated and eligible for vaginal delivery), at the Hospital Materno Infantil in Lima, Peru and low zinc intake who were carrying a singleton fetus, and had lived in coastal Peru for ≥ 6 months before pregnancy were recruited for the study. These women indicated with low zinc intake living in this region and at 10 to 24 weeks' gestation. The study protocol was approved by the institutional review boards of the Instituto de Investigación Nutricional (IIN) and The Johns Hopkins School of Hygiene and Public Health.
Interventions	1 group received a daily supplements containing 60 mg Fe (ferrous sulphate) and 250 µg folate with 15 mg of Zn (zinc sulphate) and the other received the same Fe supplement but without an additional 15 mg Zn (zinc sulphate). Women were asked to take 1 pill daily midmorning with a vitamin C–containing drink or water according to the Peruvian guideline. Supplementation began at gestation week 10–24 and continued until 4 weeks postpartum. The supplements were produced by a local pharmaceutical company (Instituto Quimioterápico, SA, Lima, Peru) in coded blister packages. To verify the formulation of the supplements and the integrity of the coding scheme, samples of each supplement type were analysed by the IIN laboratory 2 times during the study. Zinc: 15 mg zinc plus 60 mg iron plus 250 µg folate (n = 521). Non‐zinc: 60 mg iron plus 250 µg folate (n = 495).
Outcomes	Maternal outcomes Duration of pregnancy; preterm birth (< 37 weeks); very preterm birth (< 33 weeks); post‐term birth (> 42 completed weeks); serum and urinary zinc concentrations; haemoglobin; serum ferritin; fetal heart rate and movement measures. Neonatal outcomes Birthweight; low birthweight; high birthweight; cord vein zinc; cord vein haemoglobin; cord vein serum ferritin; crown‐heel length; head circumference; chest, calf and mid‐upper arm circumference; biceps, subcapsular and calf skinfold thicknesses.
Notes	Adherence: mean of about 85% of capsules consumed, which was similar across the groups. Adjustments for baseline differences in maternal age and in‐home electricity were made by multiple regression.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method of sequence generation not reported.
Allocation concealment (selection bias)	Low risk	Coded blister packages were prepared by a local pharmaceutical company, and allocation was thus concealed by use of this third party.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Investigators, other health personnel and women were blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not reported but likely to have been done due to use of placebo.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	21.5% (279/1295) women lost to follow‐up by time of giving birth ‐ 18 (1%) were found to live in another community and therefore not eligible to participate; 92 (7%) declined to participate; 71 (5%) moved out of the study area; 30 (2%) miscarried; 58 (4%) left the study for other reasons; 10 (1%) were subsequently found to have twin pregnancies or to have developed pregnancy complications.
Selective reporting (reporting bias)	Unclear risk	No information on if the protocol had been published prior to the trial.
Other bias	Low risk	No apparent risk of other bias.